1. Field of the Invention
This invention relates generally to a novel enclosure for a valve actuator, and more particularly, to an enclosure for protecting valve actuators from fire damage.
2. Description of the Prior Art
In petroleum refineries and petrochemical plants, there exist enormous amounts of flammable products being stored, pumped, and processed. These flammable products represent a very great fire hazard to all equipment where such flammable products might be present. The release of flammable products in a refinery or chemical plant can result in enormous fire damage to the plant if such flammable material is ignited. The release of flammable material can be result of the failure of a mechanical seal on a pump, the rupture of piping, the failure or leaking of a process valve, or a large number of other possible causes.
One of the primary methods in preventing large fires and in stopping them once they have started is to control the release of flammable product into the area where the fire is burning. The prevention or control of such a fire depends greatly upon cessation of the flow of flammable product before serious and irreversible damage can be done. Once the flammable product is no longer available, the fire can be easily extinguished.
In order to stop the flow of flammable products under such circumstances, many refineries and chemical plants provide isolation or block valves to shut off the flow of flammable product so that the fire can be easily extinguished. These isolation or block valves are often remote-controlled motor-operated valves. In terms of sensitivity to fire, it is usually the case that the valve actuators are more troublesome than are the valves themselves. Typically, the valves themselves used in this environment have heavy steel castings and machined parts so that they are not affected by a fire to the extent that they require protection themselves.
However, actuators of the eletromechanical type usually include soft metal, plastic parts, and sensitive electrical components that require protection from fire so that the actuator can be relied upon to activate the valve when needed, even when the valve itself is directly in the fire. Typical of the type of electromechanical valve actuator used in this environment are those sold under the designations EB-10, EB-20 and EB-30 by E. I. M. Company, Inc. of Missouri City, Tex.
A number of early attempts were made to fireproof these electromechanical valve actuators used in conjunction with isolation or block valves as part of a fire control system. One simple technique was simply to wrap the valve actuator in refractory material, for example in the form of a refractory blanket. In some cases such insulation was held in place on the actuator by a cloth bag laced together with steel cables. This method of protecting value actuators suffers from an enormous number of disadvantages. The bag itself has no structural strength and cannot withstand any significant blow or direct exposure to a fire hose stream. In addition, there is little weather resistance provided by such a cloth bag enclosure system, and there is no viable means of access to the equipment for maintenance purposes, it being difficult and tedious to unlace and replace the bag covering if the actuator requires maintenance.
There have been attempts in the prior art by both the inventor of the present invention and others to provide fire protection enclosures for electromechanical valve actuators that are built from rigid metal frames to provide adequate structural strength and are constructed of a plurality of units to provide access to various parts of the actuator for ease of maintenance and installation. However, these fire protection enclosures have suffered from a number of disadvantages. For some of the more severe applications, the structure of the refractory material used in these enclosures has been limited as to strength and weather resistance.
Additionally, these prior art fire protection enclosures have been difficult to manufacture because of the necessity of providing some means of attachment of refractory board, refractory blanket, or vacuum molded shells to the rigid frame or expanded metal sides of such framework. The prior art attempts to use vacuum molded shells that were slipped over metal frames after curing have not proved successful. Because of the size of the molded shells requuired for the actuator enclosures and the soft pliable nature of the uncured molded part, removing the molded part from the mold and handling it for transfer to a drying oven created dimensional distortions that were unacceptable in the dimensionally accurate framework of the enclosures.
It is known in the prior art to use a vacuum molding technique to produce fire protection coverings for fluid piping components such as valves, fittings, and pipe joints. An example of the application of such a vacuum molding technique is disclosed in U.S. Pat. No. 4,046,406 to Press et al. However, the fire shield disclosed in the Press patent is for fluid piping components only and provides protection only up to average flame temperatures of 1000.degree. to 1200.degree. F. Though Press discloses the use of an expanded metal skeletal structure disposed within a body of refractory material, no rigid metal frame is shown as part of the fire shield, and dimensional accuracy between each segment of the shield and between the shields and the fluid piping component is not critical. Further, there is no indication of an airtight seal between the two segments of Press' fire shield, capable of precluding a flame path into the area protected by the fire shield.
The problems and disadvantages enumerated in the foregoing are not intended to be exhaustive but rather are among many which tend to impair the effectiveness of previously known fire protection enclosures for valve actuators. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that fire protection enclosures for valve actuators appearing in the art have proven unsatisfactory in a number of respects.